Synchronizing apparatus

ABSTRACT

Synchronizing apparatus is disclosed in accordance with the teachings of the present invention wherein the operation of a first device is regulated in accordance with the operation of a second device. The phase relationship between signals representing the operation of the first and second devices, respectively, is determined by comparison means which produces a pulse width modulated signal indicative of said phase relationship. Control signal generating means responds to the pulse width modulated signal to generate an analog signal having an amplitude established by said phase relationship. Feedback means, including variable frequency generating means, is controlled by the analog signal to modify the operation of the first device whereby said first device is urged into a synchronous relationship with said second device and the signals representative of the operation of said first and second devices admit of a desired phase relationship.

United States Patent 1191 Donohue et al. I

[ SYNCHRONIZING APPARATUS [111 3,820,893 June 28, 1974 PrimaryExaminer-Samuel S. Matthews 5 I 1 mentors James I-Xmohue Joseph RAssistant ExaminerE. M. OConnor Kramer, Victor Rodek, all of J R l bRochester, NY. Attorney, Agent, or zrm-James a a ate [73] Ass1gnee: g3?Corporation, Stamford, [57] I ABSTRACT Synchronizing apparatus isdisclosed in accordance [22] 1972 with the teachings of the presentinvention wherein [21] Appl. No.: 283,672 the operation of a firstdevice is regulated in accordance with the operation of a second device.The Refined Apphcauon Dam phase relationship between signalsrepresenting the [62] Division of Sen N01 89,869- i970- operation of thefirst and second devices, respectively, is determined by comparisonmeans which produces a [52] US. Cl 355/14, 250/2l9 FR, 355/50 pulsewidth modulated signal indicative f said phase [5 i Cl. relationshipControl ignal generating means respo d Field of Search 1 3, 3i, iii,109, to the pulse width modulated signal to generate an an- 355/50; 0/ R0141391711219 alog signal having an amplitude established by said 219DR; 352/17, 20, 24 phase relationship. Feedback means,. includingvariable frequency generating means, is controlled by the [56]References Cited analog signal to modify the operation of the first de-UNITED STATES PATENTS vice whereby said first device is urged into asynchro- 1,964,874 7/1934 Frankboner 250/219 FR nous relationship withSaid Second device and the 1,969,965 8/1934 Jones 250/219 FR x al' epesentati e of the operation of said first and 2,760,] 37 8/ 1956 Andrews250/219 DR second devices admit of a desired phase relationship.3,441,342 4/1969 Ball et al 352/17 3,655,280 4/1972 Zoppoth 355/3 2Claims, 4 Drawing Figures /5 I F 2/ 20 /.9 Voltage I T Motor Amplifiergg z ii o z I I g L 32 n: J I m, i t -5, Source 1 Control SignalGenerator I 1 1s 17 /a I c 1 1 I Integrator Store v l t e I l3- gggi IGenera or L J Source 11 n n Cdntrol PATENTEDJUN28 m4 sum 3 or 4 Fig. 5.

PATENTEDJum x924 dim SHEET & 0F 4 1 SYNCHRONIZING APPARATUfi This is adivision of application Ser. No. 89,869, filed 1 1/16/70.

This invention relates to apparatus for regulating the operation of afirst device in accordance with the operation of a second device and, inparticular to apparatus for synchronizing the production of a firstsignal with that of a second signal.

The desirability of maintaining a rigid synchronous relationship betweentwo or more operating devices is common to many applications such as anindustrial assembly line,.web combining techniques, photographicprocessing, switching devices, and the like. A basic requirement of eachof these applications is to sustain a constant relationship between theoperating characteristics, such as speed, of critical devices. Forexample, in an industrial assembly line, the speed of a transportingconveyor belt must bear fixed and unvarying relationship with respect tothe operating speeds of the processing machines that act in acooperative manner therewith. Failure to maintain this relationshipresults in in misalignment of component'parts and impairment of theassembly line. Consequently, if the speed of the conveyor belt variesbecause of the effects of loading or external factors, the speed of theprocessing machines must be varied in a corresponding manner.

Similarly, where a plurality of webs are to be combined, as in anewspaper or magazine printing press, the association of a pre-printedweb with a main web must be accomplished with a minimal amount ofmisregistration. However, spacings between the indicia on the preprintedweb might differ slightly fromthe spacings between indicia on the mainweb, causing a slight error in alignment that would be rapidlycumulative and readily noticeable. Hence, the speed of insertion of thepreprinted web must be precisely regulated to obviate this error.Likewise, when a photographic print on a strip of positive film. is tobe made from an image prerecorded on negative film, movement of the twostrips must be synchronized. In many instances the negative, which hasbeen processed, has experienced a slight degree of shrinkage, therebyaltering the relationship between the picture areas. It is necessary,then, to alter the velocity of one or both of the strips to re-establishthat relationship. Additionally, if the sound and picture of sound filmsare recorded on separate carriers, it is essential that reproduction ofthe sound and the picture, or display thereof, be synchronized.

The-prior art has attempted to synchronize the operating speeds ofcooperating devices by utilizing a common source of motive power.Various speeds are ascertained by providing different speed reducingdriving gear ratios between the single motor which comprises the sourceof motive power and-each device. This tech nique suffers from thedisadvantages of being economically prohibitive and inflexible. A hightorque, constant velocity motor capable of driving each device forprolonged periods of time and highly durable gears exhibiting minimalbacklash must be employed. Adoption of this arrangement provides fixedspeed ratios between the operating devices which ratios cannot bealtered unless the individual gears of the speed reducing gears arereplaced. In addition, the introduction of an infinitesimalsynchronization error cannot be eliminated and rapidly becomescumulative. To overcome these disadvantages particular electromechanicalsynchronizing 2 systems have been designed for specific applications.Relatively few of these systems, however, are adaptable for universalservice. Thus, a system that successfully synchronizes the speed of afirst mechanical device first device in accordance with the operation ofa second device.

It is another object of this invention to provide apparatus forregulating the production of a signal by first signal producing means inaccordance with a signal produced by second signal producing means.

It is a further object of this invention to provide phasing apparatusfor eliminating a relative phase difference between a plurality ofsignals.

lt'is yet another object of this invention to provide apparatus forregulating the velocity of a first moveable member in accordance withthe velocity of a second moveable member. l

A further object of this invention is to provide apparatus forsynchronizing the operating speeds of a plurality of devices havingvariable speed ratios therebetween.

Still another object of the present invention is to provide apparatusfor synchronizing the alignment of a moveable member.

Various other objects and advantages of the invention will become clearfrom the following detailed description of exemplary embodimentsthereof, and the novel features will be particularly pointed out inconnection with the appended claims.

In accordance with this invention, apparatus for synchronizing theproduction of a first signal in accordance with the production of asecond signal is provided wherein said first and second signals areapplied to phase comparison means, said phase comparison means beingadapted to generate signals indicative of the phase relationship betweensaid first and second signals; the signals generated by the phasecomparison means are applied to control signal generating means wherebyan analog signal having an amplitude representative of said phaserelationship is generated and feedback means respo ds to said analogsignal to modify the production of s hid first signal such that saidfirst signal admits of a desired phase relationship with respect to saidsecond signal. If the first and second "signals represent the velocitiesof first and second moveable members, the feedback means may include anelectric motor for imparting a velocity to said first moveable membersuch that the speed of said electric motor is dependent upon said analogsignal whereby the velocity of said first moveable member issynchronized with the velocity of said second moveable member.

The invention will be more clearly understood by reference to thefollowing detailed description of exem-' plary embodiments thereof inconjunction with the acv companying drawings in which:

FIG. 1 is a block diagram of the synchronizing appa- FIG. 3 is agraphical representation of the waveforms generated by the apparatus ofFIG. 2; and

FIG. 4 is one exemplary embodiment of a system wherein the apparatus ofthe present invention may be utilized.

Referring now to the drawings wherein like reference numerals are usedthroughout, and in particular to FIG. 1, there is illustrated a blockdiagram of an embodiment of the synchronizing apparatus of thepresent invention which comprises first signal producing means 11, second signalproducing means 12, comparison means 13, control signal generating means14 and feedback means 15. First signal producing means 11 may comprise aconventional signal generator for providing a signal having a phasecharacteristic to be controlled in accordance with the presentinvention. The signal produced by first signal producing means 11 may bean analog signal having an ac. and/or d.c. component, or a pulse signal.As will be further described hereinbelow, the signal produced by firstsignal producing means 11 may be indicative of the speed of a firstmoveable member such as a rotating device having an angular velocity ora translating device having a rectilinear velocity. Typical examples ofthe former may comprise rotating drums or shafts, and typical examplesof-the latter may comprise a strip of recording medium or endless belt.Those skilled in the art will recognize that the speed of a movingmember may be indicated by providing one or a plurality of indexingmeans on said moving member and sensing means for detecting the passageof said indexing means through a predetermined position. Thus, if saidmoving means comprises a rotating device, said indexing means maycomprise an electrically conductive strip mounted on the periphery ofsaid rotating device and said sensing means may comprise an electricalcontact whereby an electrical circuit is completed each time saidconductive strip rotates into the vicinity of said electrical contact.Similarly, said indexing means may comprise a light-reflecting strip ora sense marking adapted to modulateradiant energy and said sensingmeansmay comprise a photocell responsive to the increase in theintensity of the light reflected by said light-reflecting strip or tothe modulation of radient energy by said sense marking. If said movingmeans comprises a trans lating device, the indexing means may be similarto those aforedescribed and spaced uniformly along the length of saidmoving means.

Second signal producing means 12 may be similar to first signalproducing means 11; however, as will soon become apparent, the phasecharacteristic of the signal produced by said second signalproducingmeans 12 need not be controlled and, for the purpose of thepresent description, may act as a reference for controlling the signalproduced by said first signal producing means 11. Hence, second signalproducing means 12 may comprise a reference signal generator, well knownto those skilled in the art. Comparison means 13 is coupled to the firstand second signal producing means 11 and 12, respectively, and isadapted to determine the phase relationship between the signalsrespectively supplied thereto, and to generate signals indicative ofsaid phase relationship. Accordingly, comparison means 13 may comprise aconventional phase detecting circuit wherein the signal produced bysecond signal producing means 12 is utilized as a reference signal.Comparison means 13 may comprise pulse duration modulation means forgenerating a pulse signal having a time duration proportional to thedifference between the phases of the signals supplied thereto. Theforthcoming description of FIG. 2 will specify one embodiment of suchpulse duration modulation means.

Control signal generating means 14 is coupled to comparison means 13 andserves to provide a control signal having a magnitude determined by thesignals generated by said comparison means 13. As illustrated in FIG. 1,control signal generating means 14 may comprise integrating means 16coupled to storage means 17 which, in turn, is coupled to a controlvoltage generator 18. Integrating means 16 may comprise a conventionaloperational amplifier integrating circuit of the type well known in theprior art. Alternatively, integrating means 16 may comprise a low-passR-C circuit or, if desired, a digital integrating circuit. In addition,integrating means 16 preferably includes means to reset the outputsignal thereof to an initial condition. Storage means 17 is adapted tostore the maximum amplitude obtained by the integrated signal providedby integrating means 16 and may comprise an analog storage device suchas a grounded capacitor or other conventional analog storage means, or adigital storage device such as a storage register or magnetic storagedevice. A specific embodiment of storage means 17 will subsequently bedescribed and the manner in which the maximum amplitude obtained by theintegrated signal is stored will be explained in detail. However, itshould be understood that, for-the purpose of describing the blockdiagram of FIG. 1, storage means 17 may comprise a conventional sampleand hold network.

The control voltage generator 18 coupled to storage means 17. is adaptedto provide the control signal referred to hereinabove. and may compriseamplifying means to amplify the signal supplied thereto by storage means17 to a desired value. In the absence of a stored signal, controlvoltage generator 18 provides at its output terminal, a dc. voltage ofconstant amplitude for a purpose soon to become apparent. It isrecognized that if the amplitude of the signal stored by'storage means17 is of a sufficient magnitude, the control voltage generator 18 may beomitted.

Integrating means 16 and storage means 17 are additionally coupled tosequence control means 22 and are supplied with operating controlsignals therefrom. The operating control signal supplied to integratingmeans 16 from sequence control means 22 is adapted to reset theintegrating means 16 to its initial condition. Further, the operatingcontrol signal supplied to storage means 17 serves to enable the storagemeans 17 to store the maximum amplitude obtained by the integratedsignal. Hence, if storage means 17 comprises a sample and hold network,the operating control signal supplied thereto may be analogous to asampling signal. Accordingly, sequence control means 22 may comprise adigital logic circuit that automatically generates the aforementionedoperating control signals when comparison means 13 has determined thephase relationship between the signals produced by first and secondsignal producing means 11 and 12, respectively. A

v more detailed discussion of sequence control means 22 is set forthbelow in conjunction with the description of FIG. 2. g

I The output of control signal generating means 14 is coupled tofeedback means 15, the latter being adapted to modify the operation ofthe first signal producing means lll in accordance with the controlsignal provided by control signal generating means 14. Feedback meanscomprises variable frequency generating means 19 having an outputcoupled to modifying means 21 via amplifier 20. The variable frequencygenerating means 19 is supplied with the control signal generated bycontrol signal generating means 14 and is capableof producing a periodicsignal having a frequency determined by the magnitude of said controlsignal. Hence, variable frequency generating means 19 may compriseconventional frequency modulating means such as a voltage controlledoscillating means. Modifying means 21 is coupled to the first signalproducing means 11 and serves to alter the operating characteristics offirst signal producing means lll whereby the phase of the signalprovided by first signal producing means 111 is altered in accordancewith the periodic signal produced by variable frequency generating means19. Accordingly, if the first signal producing means lll comprises amoveable member as described hereinabove, modifying means 21 maycomprise an electric motor mechanically coupled to the moveable memberand operative to impart a velocity thereof. It is evident that the speedof the moveable member is proportional to the angular velocity of theelectric motor, and the angular velocity of the electric motor isdependent upon the frequency of the signal applied thereto. The electricmotor may comprise a synchronous motor. It is, of course, understoodthat modifying means 21 may comprise an electric motor whose angularvelocity is dependent upon the magnitude of the signal applied thereto.in that case, the variable frequency generating means 19 may be omittedand the output of control signal generating means 114 coupled directlyto amplifier or, alternatively, control signal generating means 14 maybe coupled to a conventional amplitude modulating means.

The operation of the apparatus illustrated in FIG. 1 will now bedescribed. It will be initially assumed that first and second signalproducing means, ll and 12,

comprise first and second moveable members having velocities impartedthereto by first and second driving means, respectively. It will befurther assumed that the velocities of the first and second moveablemembers are not necessarily equal. As was described hereinabove, thevelocity of the first moveable member may be indicated by signals whichare produced by first sensing means fixedly located in afirstpredetermined position when the indexing means includable in the firstmoveable member traverse said first predetermined position. Hence, thefrequency of the signals produced by first signal producing means ll isdirectly related to the velocity of the first moveable member.Similarly, the velocity of the second moveable member may be indicatedby signals which are produced by second sensing means fixedly located ina second predetermined position when indexing means includable in thesecond moveable member traverse said second predetermined position. Thefrequency of the signals produced by second signal producing means 12 isdirectly related to the velocity of the'second moveable member. Theratio of the spacing between the consecutive indexing means of the firstmoveable member to the spacing between the consecutive indexing means ofthe second moveable member should be equal to the ratio of .the velocityof the first moveable member to the velocity of the second moveablemember. Accordingly, the frequencies of the signals applied tocomparison means 13 will be equal, notwithstanding the differentvelocities represented thereby, when the velocity of the first moveablemember is synchronized with the velocity of the second moveable member.1

If the signals applied tocomparison means 13 are pulses, comparisonmeans 13 produces a pulse having a time duration equal to the phasedifference between the leading edges of the applied pulses. If thesignals applied to comparison means 13 are ac. signals, comparisonmeans13 may additionally include zero crossing detecting means to generateimpulses at the zero crossing timesof the applied signals. A pulsehaving a time duration equal to the phasev difference between] thegenerated impulses may then be produced. The pulse produced bycomparison means l3 may admitof a first polarity when the signalsupplied by the first signal producing means llll exhibits a phaseleading relationship with respect to'the signal supplied by the secondsignal producing means 12; and, conversely, the pulse produced bycomparison means 13 may admit of a second polarity when the signalsupplied by the first signal producing means lll exhibits a phaselagging relationship with respect to the signal supplied by the secondsignal producing means 12. It is, therefore, understood, that when thealignment of a first moving member admits of a desired relationship withrespect to the alignment of a second moving member, the signals appliedto comparison means 13 are in phase and comparison means 13 does notproduce a pulse. If the signals applied to phase comparison means 113maintain a phase coincidence relationship throughout a substantialinterval'of time, it can be deduced that the velocity of the firstmoving member is in synchronism with the velocityof the second movingmember. An exemplary embodiment of comparison means 13 is describedbelow with respect to FIG. 2, and one skilled in theart will readilyperceive several equivalents thereof.

The pulse produced by comparison means l3 is ap plied to integratingmeans 16 of control signal generating means 14. As is understood, theintegral of a pulse signal will approximate a linearly increasing signalsuch as a ramp signal or sawtooth waveform, having a slope proportionalto the amplitude of the pulse signal. The

maximum amplitude obtained by the integrated signal during eachintegrating cycle is established by the duration of the pulse signal.Hence, if the pulse produced by comparison means 13 is of positivepolarity, the slope 1 of theintegrated signal is positive and,conversely,-if

the pulse produced by comparison means 13 is of negative polarity, theslope of the integrated signal is negative. When the integrated signalobtains its maximum amplitude, sequence control means 22, in a manner tobe described, enables storage means 17 to store said maximum amplitude.If storage means 117 comprises an analog storage device, such as agrounded capacitor, it should be apparent that the amplitude of thesignal stored thereby represents an error signal indicative of the phaserelationship between the signals produced by the first and second signalproducing means l1 and 112, respectively, and the polarity of the storedsignal represents a leading or lagging phase relationship. At apredetermined period of time subsequent to the storing of the integratedsignal, sequence control means 22, in a manner described below, appliesa reset signal to integrating means M to reset the integrating means toan 7 initial condition whereby a succeeding integrating cycle may beeffected.

The error signal stored by storage means 17 is amplified by controlvoltage generator 18, which may comprise amplifying means, and appliedto the variable frequency generating means 19 of feedback means 15. Itis preferred, in some applications of the present invention, to providea medial frequency about which the frequency of the periodic signalproduced by variable frequency generating means 19 will vary inaccordance with the error signal stored by storage means 17. Therefore,control voltage generator 18 may include combining means such as asumming amplifier to combine the error signal with a nominal orthreshold voltage which corresponds to said medial frequency.Accordingly, the control signal applied to variable frequency generatingmeans 19 will vary about a threshold level in accordance with the errorsignal stored by storage means 17. When the integrated signal applied toand stored by storage means 17 is zero, i.e., when the signals appliedto comparison means 13 are in phase, control voltage generator 18 willsupply the variable frequency generating means 19 with the nominal orthreshold voltage, The periodic signal produced by variable frequencygenerating means 19 is amplified by amplifier and applied to modifyingmeans 21 as a supply signal therefor. If modifying means 21 comprises anelectric motor, the angular velocity thereof is dependent upon thefrequency of the supply signal.

It should now be readily apparent that when the alignment of a firstmoveable member admits of a desired relationship with respect to thealignment of a second moveable member, the signals produced by the firstand second signal producing means 11 and 12, respectively, are in phase.If said desired relationship is maintained over an interval of time, thevelocity of said first moveable member is in synchronism with thevelocity of said second moveable member. Comparison means 13 does notproduce a pulse and the output of the integrating means 16 is zero.Accordingly, the error signal stored by storage means 17 is zero andcontrol voltage generator l8'applies a nominal or threshold voltage tothe variable frequency generating means 19. Consequently, the frequencyof the signal supplied to the electric motor by the variable frequencygenerating means 19 is unchanged and the motor continues to drivethefirst moveable member at the synchronized speed. If, however, the speedof the first moveable member is decreased because of external influence,or if the speed of the second moveable member is increased, the signalsproduced by the first sig'nal producing means 11 will be applied tocomparison means 13 in a phase lagging relationship with respect to thesignals produced by the second signal producing-means 12. Accordingly,comparison means 13 produces a pulse of a first polarity which, solelyfor the purpose of explanation, may be assumed to be positive, having aduration equal to the difference in the phases of the signals appliedthereto. Integrating means 16 integrates the pulse produced bycomparison means 13 to derive an analog signal representative of thephase relationship of the signals produced by the first and secondsignal producing means 11 and 12, respectively. The maximum amplitudeobtained by the analog signal during the integrating cycle comprises anerror signal that is applied to and stored by storage means 17. Theerror signal, which is here assumed to be of positive polarity,

is added to the nominal or threshold voltage, by control voltagegenerator 18 to produce a control signal that is aupplied to variablefrequency generating means 19. The frequency of the periodic signalproduced by variable frequency generating means 19 exceeds the medialfrequency by an amount determined by the error signal, thereby drivingthe electric motor at an increased angular velocity. Consequently, thespeed of the first moveable member is increased to advance the phase ofthe signal produced by first signal producing means 11, whereby theerror signal is reduced to a null value and proper alignment of thefirst moveable member is obtained. If, now, the speed of the firstmoveable member is increased because of external influences, or if thespeed of the second moveable member is decreased, thereby altering therelative alignment of said first moveable member the signals produced bythe first signal producing means 11 will be applied to comparison means13 in a phase leading relationship with respect to the signals producedby the second signal producing means 12. Accordingly, comparison means13 produces a pulse of a second polarity, which, solely for the purposeof explanation, may be assumed to be negative, having a duration equalto the difference in the phases of the signals applied thereto.Integrating means 16 integrates the pulse produced by comparison means13 to derive an analog signal representative of the phase relationshipof the signals produced by the first and second signal producing means11 and 12, respectively. The maximum amplitude obtained by the analogsignal during the integrating cycle comprises an error signal that is'applied to and stored by storage means 17. The error signal, which ishere assumed to be of negative polarity, is subtracted from the nominalor threshold voltage by control voltage generator 18 to produce acontrol signal that is supplied to variable frequency generating means19. The frequency of the periodic signal produced by variable frequencygenerating means 19 is less than the medial frequency by an amountdetermined by the error signal, thereby driving the electric motor at adecreased angular velocity. Consequently, the speed of the firstmoveable member is decreased to retard the phase of the signal producedby first signal producing means 11, whereby the error signal is reducedto a null value and proper alignment of the first moveable member isobtained.

It should be understood that the present invention is not limited to theembodiment employing first and second moveable members and an electricmotor. For example, the second signal producing means 12 may comprise areference signal oscillator for producing reference signals with whichto synchronize the speed of the first moveable member. In addition,first signal producing means 11 may include a device other than amoveable member, such as a variable frequency generator or variabledelay generator, thereby obviating the need for an electric motor.

FIG. 2 is a schematic diagram of a portion of the apparatus that may beutilized in the embodiment of FIG. 1 and comprises comparison means 13,integrating means 16, storage means 17, control voltage generator 18 andsequence control means 22. Comparison means 13 comprises first andsecond bistable multivibrators 131 and 132, respectively, and first andsecond coinci dence means 133 and 134, respectively. Each bistablemultivibrator is provided with first and second input terminals andfirst and second output terminals and is 9 capable of assuming a firstor second output state in accordance with the signals applied to theinput terminals thereof. The first input-terminal of bistablemultivibrator 131 is adapted to be provided with a pulse signal such asa pulse signal derived from first signal producing means 11 of FIG. 1.Similarly, the first input terminal of bistable multivibrator 132 isadapted to be provided with a pulse signal such as a pulse signalderived from second signal producing means 12. Coincidence means 133 maycomprise a conventional AND gate and includes a first input terminalcoupled to a first output terminal of bistable multivibrator 131 and asecond input terminal coupled to a second output terminal of bistablemultivibrator 132. Coincidence means 134 is similar to the coincidencemeans 133 and includes a first input terminal coupled to a first outputterminal of bistable multivibrator 132 and a second input terminalcoupled to a second output terminal of bistable multivibrator 131. I

Bistable multivibrators 131 and 132 initially assume their second outputstates, respectively. Accordingly,

each of coincidence means 133 and 134 is provided with a signal at thesecond input terminal thereof. If a pulse signal is applied to the firstinput terminal of bistable multivibrator 131 prior to the application ofa pulse signal to the first inputterminal of bistable multivibrator 132,bistable multivibrator 131 will assume its first output state, therebyproviding coincidence means 133 with a signal at the first inputterminal thereof and removing the signal previously provided at thesecond input terminal of coincidence means 134. Hence, coincidence means133 will initiate an output pulse signal when the pulse applied tobistable multivibrator 131 exhibits a leading phase relationship withrespect to the pulse applied to bistable multivibrator 132. Whenbistable multivibrator 132 is subsequently provided with a pulse at thefirst input terminal thereof, bistable multivibrator 132 will assume itsfirst output state, thereby removing the signal previously provided. atthe second input terminal of coincidence means 133, causing the outputpulse signal initiated by coincidence means 133 to terminate. it shouldnow be readily apparent that if the pulse applied to bistablemultivibrator 131 exhibits a lagging phase relationship with respect tothe pulse applied to bistable multivibrator 132, the comparison means 13operates in a manner complementary to that just described wherebycoincidence means 134 produces an output pulse signal having a timeduration equal to the time delay between the pulses applied to bistablemultivibrators 132 and 131, respectively.

Integrating means 16 includes first and second integrating circuits. Thefirst integrating circuit comprises an'input resistance means 160,amplifier means 163, capacitance means 164 and switch means'166.Resistance means 160 couples coincidence means 133 to amplifier means163, and exhibits a resistance of R and exhibits a capacitance of Cmicrofarads. A switch means 166 is connected in parallel relationshipwith capacitance means 164. As is understood by those skilled in theart, the closing of switch means 166'is effective to dischargecapacitance means 164 thereby resetting the first integrating means toan initial state. Hence, an

integrating cycle may be terminated by the closure of switch means 166.Switch means 166 may comprise a solid-state switch, such as a switchingtransistor, or may comprise one of a plurality of armatures of resetrelay means 228, further described below. It is clear that if a pulsesignal is applied to resistance means 160, the pulse signal will beintegrated by the first integrating circuit, resulting in a ramp signalhaving a constant slope equal to the productof the amplitude of thepulse signal and the inverse of the time constant (RC) of theintegrating circuit. At the termination of the pulse signal applied tothe resistance means 160, the amplitude obtained by the ramp signal isequal to the product of the slope thereof and the time duration of theapplied pulse signal. Hence, the signal at the output of amplifier Imeans 163 is an analog signal representative of the duration of an inputpulse signal applied thereto.

The second integrating circuit of integrating means 16 is similar to thejust described first integrating circuit and comprises an inputresistance means 159, amplifier means 161, capacitance means 162 andswitch means 165. Resistance means 159, having a resistance R, couplescoincidence means 134 to amplifier means 161, the latter being similarto amplifier means 163. Feedback capacitance means 162 couples theoutput of amplifier means 161 to the input thereof and exhibits acapacitance of C microfarads. Switch means 165, which is simlar toswitch means 166, is connected in parallel relationship with capacitancemeans 162 and is adapted to discharge capacitance means 162 therebyresetting the second integrating means to an initial state. The secondintegrating means serves to integrate a pulse signal applied toresistance means 159, resulting in a ramp signal having a constant slopeequal to the product of the amplitude of the pulse signal and theinverse of the time constant (RC) of the integrating circuit. Upon thetermination of the pulse signal applied to resistance means 159, theamplitude obtained bythe ramp signal is equal to the product of theslope thereof and the time duration of the applied pulse signal. Itshould be realized that each of amplifier means 161 and 163 may be sochosen, or the bias thereof so adjusted, that the ramp signal producedby the amplifier means obtains a saturation voltage prior to thetermination of the pulse signal applied to the amplifier means. As willsoon become apparent, this limits the maximum amplitude of the errorsignal stored by storage means 17.

For a purpose soon to be understood, it is desired to convert thepolarity of the analog signal produced by amplifier means 163.Accordingly, polarity inverting means comprised of amplifier means 167and resistance means 163 nd 169 is provided, wherein resistance means166 couples amplifier means 163 to amplifier means 167 and resistancemeans 169 is a feedback resistor interconnecting the'output of amplifiermeans l 1 comprise a solid-state switch, such as a switching transistor,or may be one of a plurality of armatures of sample relay means 226,further described below. Switch means 173 is adapted to be closed for asufficient period of time to enable grounded capacitance means 171 tocharge to the level of the inverted analog signal appearing at theoutput of amplifier means 167;and switch means 174-is adapted to beclosed for a sufficient period of time to enable grounded capacitancemeans 172 to charge to the level of the analog-signal appearing at theoutput'of amplifier means 161,

Control voltage generator 18 comprises amplifier means 181, resistancemeans 182-185 and adjustable resistance means 186. Amplifier means 181is-similar to aforedescribed amplifier means 163 and may-comprise anoperational amplifier. Resistance means 182 couplesgrounded capacitancemeans 172 to amplifier means 181, resistance means 183 couples groundedcapacitance means 171' to amplifier means 181 and resistance means 184couples adjustable-resistance means 186 to amplifier means 181. Inaddition, resistance means 185' isa feedbackresistor interconnecting theoutput of amplifier means 181 to the input thereof. Ad-

justable resistance means 186 is adapted to beprovided 1 with a constantsupply voltage V and may comprise a potentiometer having 'an adjustablecontact 187. Hence, the magnitude of .the voltage applied to resistancemeans 184 is'dependent upon the-position of adjustable contact 187. Inthe'illustrated configuration,

amplifier means 181 servesto algebraically combine each of resistancemeans 182,

" duce a signal at anoutput'terminal thereof when the inputfterminalsthereof are provided with coinciding input signalsxFirst and secondinput terminals of coincidence means 223 are coupled to level invertingmeans 221 and 222, respectively. A thirdinputterminal of coincidencemeans 223 is coupled to the-first output terminal of bistable'rnultivibrator-229. The latter issimilar' to aforedescribed bistablemultivibrator 131, and includes first and second input terminalsselectively provided with an activating signal from source '+V bycomplementary switch means 233 and 234. Switchm'eans'233 normallyassumes a closed state and may comprise a' solid-state switch, such as aswitching transistor, ormay comprise one of a plurality of annatures ofresetrelay means 228. Switch means 234 normally assumes an open stateandmay' comprise a solidstate switch, such as a switching transistor, ormay comprise one of aplurality of armatures of reset relay means 228. cr

The output terminal of coincidence means 223 is bistablemultivibrator'224 is coupled to an input terminal of coincidence means227. Accordingly, bistable multivibrator 224 is effective to assume afirst output state when bistable multivibrator 230 assumes a firstoutput state and to assume a second output state when bistablemultivibrators 131 and 132 are reset to their respective second outputstates. 7

Coincidence means 225 is similar to aforedescribed coincidence means 223and includes additional input terminals respectively coupled to thefirst output terminals of bistable, multivibrators 131 and .132. Theoutput terminal of coincidence means 225 is coupled to the energizingcoil of sample relay means 226 and is adapted to activate said relaymeans when the analog signal produced by integrating means 16 hasobtained its maximum amplitude during an integrating cycle. It isunderstood that the output terminal of coincidence means 225 mayalternatively be coupled to the activating input terminal of asolid-state switch means.

Coincidence means 227 is similar to coincidence means 223, describedhereinabove, and includes an additional input terminal coupled to thesecond output terminal of bistable multivibrator 230. Bistablemultivibrator 230 is similar to bistable multivibrator 229 and includesfirst and second input terminals selectively provided. with anactivating signal from source +V by complementary switch means 231 and232. Switch means 231 normally assumes a closed state and may comprise asolid-state switch, such as a switching transistor, or may comprise oneof a plurality of armatures of sample relay means 226. Switchmeans232normally assumes an open state and maycomprise a solid-state switch,such as a switching transistor, or may comprise one of a plurality ofarmatures of sample relay means 226. The output terminal of coincidencemeans 227 is coupled to the energizing coil of reset relay means 228 andis adapted to-activate said relay means subsequent to the storing bystorage means 17 ofthe. analog signal produced by integrating means 16.The output terminal of a coincidence means 227 may be coupled, in thealterna'tive, to.the activating input terminal ofa solidstate switchmeans, as is readily appreciated.

The operation of the apparatus of FIG. 2 will now be described inconjunction with the explanatory waveform diagram of FIG. 3wherein'primed reference-numeralslidentify the waveforms produced bycorresponding elements identified by umprimed reference numerals.Initially, each bistable multivibrator assumes its second output state,the first and second integrating circuits of integrating means 16 arereset to their initial states, respectively, and switch means 172 and173 are open. It will first be assumed that a pulse signal I is appliedto the first input terminal of bistable multivibrator coupled to thesecond input terminal of each of bistable multivibrators 131 and 132 andis adapted to reset said bistable multivibrators to their respectivesecond output states. The outputterminal of coincidence means 223 isadditionally coupled to the second input terminal ofbistablemultivibrator 224 whose second output terminal'is coupled to aninput terminal of coincidence means 225. The first input terminal ofbistable multivibrator 224 is coupled to the first output terminal ofbis- 131 prior to the application of a pulse signal ll to the firstinput terminal of bistable multivibrator 132. It is recalled that thisoccurrence indicates that the relative alignment of a first moveablemember is displaced in a leading relationship with respect to a secondmoveable member. Stated otherwise, the signal produced by the firstsignal producing means 11 of FIG. 1 is in a phase leading relationshipwith respect to the signal produced by the second signal producing means12 of FIG. 1. Bistable multivibrator 131 responds to pulse signal I toassume its first output state as indicated at 131' Accordingly,coincidence means 133 responds to the first output state of bistablemultivibrator 131 and the sectable multivibrator 230; and the firstoutput terminal of ond output state of bistable multivibrator 132 topro- 13 duce a pulse 133. The pulse 133' is applied to resistance means160 and the first integrating circuit of integrating means 16 proceedsto integrate the pulse 133'. The polarity of the integrated signal isinverted by amplifier means 167, or an equivalent polarity invertingmeans, to produce the ramp signal 167' having negative slope. Asindicated in FIG. 3, the ramp signal produced by the first integratingcircuit obtains a saturation voltage prior to the termination of pulse133. it is observed that when coincidence means 133 is provided with twoinput signals, coincidence means 134 is inhibited from producing anoutput signal. Consequently, resistance means 159 of the secondintegrating circuit is not provided with a signal and the output ofamplifier means 161 maintains the initial state thereof.

When the pulse II' is applied to the first input termi nal of bistablemultivibrator 132 at a time t seconds subsequent to the occurrence ofpulse l, bistable multivibrator 132 assumes its first output state, asmam-- fested by the signal 132. Accordingly, the signal previouslyapplied to the second input terminal of coincidence means 133 is removedtherefrom and pulse 133' produced by coincidence means 133terminates.

When bistable multivibrator 132 assumes its first output state,coincidence means 225 is provided with an input signal at each inputterminal thereof, thereby generating an output signal to energize samplerelay means 226 as indicated-at 226'-. The energization of sample relaymeans 226 closes all open armatures thereof and opens all closedarmatures. Hence, switch means 232 provides an activating signal fromsource +V to the first input terminal of bistable multivibrator 230 andswitch means 231 removes the activating signal supplied to the secondinput terminal of said bistable multivibrator. Bistable multivibrator230 then assumes its first output state, as illustrated by the pulse230. The slight timedelay between the leading edges of pulse 226' andpulse 230 is attributed to the inherent delay of the energizing coil ofsample relay means 226. In addition, switch means 173 and 174 apply theanalog signals produced by amplifier means 167. and 161 to groundedcapacitance means 171 and 172, respectively. Since an analog signal isproduced only at the output of amplifier means 167, grounded capacitancemeans 171 is supplied with an analog signal 167' whose magnitude isproportional to the phase difference between pulses I and II, and whosepolarity represents a phase leading relationshipThe analog signal storedby grounded capacitance means 172 is effective'ly zero. It should herebe noted that, even if the ramp signal produced by the first integratingcircuit does not obtain a saturation voltage, the maximum voltageobtainable by the ramp signal occurs at the termination of the pulse 133and is equal to the product of the slope of the ramp signal and theduration t of pulse 133. Thus, the error signal 171 stored by groundedcapacitance means 171 is equal to the maxioutput terminal of bistablemultivibrator 224 is removed therefrom. Hence,'coincidence means 225 isdeactivated and sample relay means 226 is deenergized as shown at 226.The slight delay between the leading edge of pulse 224 and the trailingedge of pulse 226 is attributable to the inherent delay in the responseof the energizing coil of sample relay means 226. Switch means 173,174,231 and 232 assume the positions illustrated in FIG. 2 as a result ofthe deenergization of sample relay means 226. Consequently, the outputof amplifier means 167 is removed from grounded capacitance means 171.The error signal stored by grounded capacitance means 171 maintains asubstantially constant value, because of the low inherent leakagecharacteristics of capacitance means 171. The leakage characteristicsmay be further improved by connecting a conventional voltage followercircuit to capacitance means 171. The error signals stored by groundedcapacitance means 171 and 172 are algebraically combined by amplifiermeans 181 with a nominal or threshold voltage V derived at adjustablecontact 187, to produce the control signal 181'. It should be recognizedby one skilled in the art that the rate of change of the magnitude ofcontrol signal 181' may be limited by providing a filter capacitor inparallel relamum voltage obtained by the ramp signal during theintionship with resistance means 185. In addition, the closing of switchmeans 231 and opening of switch means 232 resets bistable multivibrator230 to its second output state. Coincidence means 227 is, therefore,provided with an input signal at each input terminal thereof, therebygenerating an output signal to energize reset relay means 228 asindicated at 228'. The energizing of reset relay means 228 closes allopen armatures thereof and opens all closed armatures. Hence, switchmeans 234 provides an activating signal from source +V to the firstinput terminal of bistable multivibrator 229 and switch means 233removes the activating signal supplied to the second input terminal ofsaid bistable multivibrator. Bistable multivibrator 229 then assumes itsfirst output state, as illustrated by the pulse 229. The slight timedelay between the leading edges of pulse 228 and pulse 229 is attributedto the inher ent delay of the energizing coilof reset relay means 228.In addition, switch means and 166 discharge capacitancemeans 162 and 164to'reset the first and second integrating circuits of integrating means16 to their initial conditions, as indicated at 16, thereby terminatingthe integrating cycle.

When bistable multivibrator 229 assumes its first output state,coincidence means 223 is provided with pulse 229' at an input terminalthereof. The remaining input terminals of coincidence means 223 areprovided with input signals by level inverting means 221 and 222,respectively, when pulses l and II terminate. At that time, coincidencemeans 223 produces an output signal assume the positions illustrated inFIG. 2. Consequently, bistable multivibrator 229 is reset to its secondoutput state, and the apparatus of FIG. 2 is now operable to respond tosubsequently applied signals.

Thus, it is seen that when a signal produced by first signal producingmeans 11 is in 'a phase leading relation'ship-with respect to the signalproduced by second signal producing means 12, coincidence means 133produces pulse 133' having a time duration representative of the phaserelationship. The time duration of pulse 133' is transformed to ananalog signal by the first integrating circuit of integrating means 16,and the polarity of the analog signal is inverted by amplifier means 167to produce the analog signal 167'. Grounded capacitance means 171 storesthe maximum value obtained by analog signal 167 during the integratingcycle, as an error signal 171. The error signal 171 is algebraicallycombined with a nominal or threshold voltage V by amplifier means 181 toproduce a control signal 181 which is applied to feedback means 15. Thefeedback means 15 modifies the operating characteristics of firstsignalproducing means 11 in a manner that tends to synchronize thesignal produced by first signal producing means 11 with the signalproduced by second signal producing means 12.

When the first signal producing means 11 is synchronized with the secondsignal producing means 12, the leading edges of pulses I and Ilcoincide. Accordingly, bistable multivibrators 131 and 132 aresimultaneously set to their respective first output states, as indicatedat 131 and 132. Consequently, coincidence means 133 and 134 remain intheir quiescent states and neither resistance means 159 nor resistancemeans 160 are provided with signals. Hence, the analog signal producedby each integrating means 16 is zero. Coincidence means 225 responds tothe first output state assumed by bistable multivibrator 131, the firstoutput state assumed by bistable multivibrator 132 and the second outputstate maintained by bistable multivibrator 224 to energize sample relayvmeans 226. Energization of sample relay means 226 closes switch means173, 174 and 232, and opens switch means 231. Grounded capacitance means171 and 172 store the analog signals produced by the first and secondintegrating circuits. In addition, bistable multivibrator 230 is set-toits first output state, as illustrated at 230, which, in turn, setsbistable multivibrator 224 to its first output state, as indicated at224. Coincidence means 225 is thereby deactivated and sample relay means226 is de-energized. Switch means 173, 174, 231 and 232 resume thepositions illustrated in FIG. 2 and the error signals stored by groundedcapacitance means 171 and 172, the amplitudes of which are equal tozero, arealgebraically combined, by amplifier means 181, with thenominal or threshold voltage V to produce the control signal 181 havinga magnitude equal to V The closing of switch means 231 resets bistablemultivibrator 230 to its second output state which coincides with the.first output state assumed by bistable multivibrator 224. Coincidencemeans 227 is thus provided with a signal at each input terminal thereofto energize reset relay means 228. Energization of reset relay means 228closes switch means 165, 166 and 234 and opens switch means 233. Theclosing of switch means and 166 has no appreciable effect on the firstand second integrating circuits of integrating means 16 inasmuch as theintegrating circuits had not been disturbed from their initial states.However, the closing of switch means 234 sets bistable multivibrator 229to its first output state. When pulses I and II terminate, coincidencemeans 223 receives a signal at 16 each input terminal thereof toeffectuate the resetting of bistable multivibrators 131, 132 and 224 totheir respective second output states. Pulse 224 is removed from theinput terminal of coincidence means 227 and reset relay means 228 isde-energized. Switch means 165, 166, 233 and 234 assume the positionsshown in FIG. 2 and bistable multivibrator 229 to reset to its secondoutput state. It is thus seen, that when the time of occurrence of pulseI is in synchronism with the time of occurrence of pulse II, the controlsignal 181 maintains thenominal or threshold level and does not varythereabout.

If, now, the signals produced by first signal producing meansll exhibita lagging phase relationship with respect to the signals produced bysecond signal producing means 12 as, for example, when the proportionalspeed of a second moveable member exceeds that of a first moveablemember such that the relative alignment of. said first moveable'memberis displaced in a lagging relationship with respect to said secondmoveable member, pulse II will be applied to the first input terminal ofbistable multivibrator 132 prior to the application of pulse I to thefirst input terminal of bistable multivibrator 131. Accordingly bistablemultivibrator 132 assumes its first output state as indicated at 132 andcoincidence means 134 is provided with a signal at each input terminalthereof. Therefore, coincidence means 134 applies a pulse signal 134' toresistance means 159 of the second integrating circuit of integratingmeans 16. The second integrating circuit integrates pulse 134 to producethe analog signal 161 at the output of amplifier means 161. It isassumed, merely for the purpose of explanation, that the analog signal161 does not obtain a saturation voltage prior to the termination ofpulse 134.

When the pulse 1' is applied to the first input terminal of bistablemultivibrator 131 at a time t seconds subsequent to the occurrence ofpulseII, bistable multivibrator 131 assumes its first output state toproduce pulse 131'. Accordingly, the signal previously supplied by thesecond output terminal of bistable multivibrator 131 to an inputterminal of coincidence means 134 is removed therefrom, causing pulse134 to terminate. It is understood that when pulse 134' terminates, theslope of the integral thereof is reduced to zero and the amplitude ofthe analog signal 161 maintains a constant value until the secondintegrating circuit is reset to its initial condition. The assumption oftheir respective first output states by bistable multivibrators 131 and132, and the assumption of the second output state by bistablemultivibrator 224 activates coincidence means 225 to energize samplerelay means 226, as indicated at 226'. The energization of sample relaymeans 226 closes all open armatures thereof and opens all closedarmatures. Hence, as previously described with reference to theoccurrence of pulse 1 in phase-leading relationship with respect to theoccurrence of pulse II, switch means 232 provides an" activating signalto the first input terminal of bistable multivibrator 230 from source +Vto set bistable multivibrator 230 to its first output-state as indicatedat 230. In addition, switch means 173 and 174 apply the analog signalsproduced by amplifier means 167 and 161 to grounded capacitance means171 and 172, respectively. The analog signal produced by amplifier means167 is effectively zero and, therefore, only grounded capacitance means172 is supplied with an analog signal 161' whose magnitude isproportional to the phase difference t between pulses I and II, andwhose polarity represents a lagging phase relationship. Thus, groundedcapacitance means 173 stores an error signal 172 equal to the maximumvoltage obatined by analog signal 161.

The assumption of its first output state by bistable multivibrator 230provides pulse 230 to the first input terminal of bistable multivibrator224, thereby setting the latter to its first output state, as indicatedat 224', and removing the signal applied by the second output terminalof bistable multivibrator 224 to an input terminal of coincidence means225. Hence, coincidence means 225 is deactivated, thereby de-energizingsample relay means 226, as illustrated by the termination of pulse 226'.Consequently, the electrical path between amplifier means 161 andgrounded capacitance means 172 is interrupted. The error signal 172stored by grounded capaitance means 172 is algebraically combined byamplifier means 181 with the nominal or threshold voltage V derived atadjustable contact 187, to produce the control signal 181. In addition,the

de-energization of sample relay means 226 closes switch means 231 toreset bistable multivibrator 230 to its second output state. Coincidencemeans 227 is, therefore, provided with an input signal at each inputterminal thereof, and generates an output signal to energize reset relaymeans 228 as indicated at 228. The enegization of reset relay means 228closes switch means 234 to provide an activating signal from source +Vto the first input terminal of bistable multivibrator 229, therebysetting bistable multivibrator 229 to its first output state, asillustrated by the pulse 229. In addition, switch means 165 and 166discharge capacitance means 162 and 164, respectively, to terminate theintegrating cycle and reset the first and second integrating circuits ofintegrating means 16 to their respective initial conditions.

When pulses I and II terminate, coincidence means 223 is provided withan input signal from level inverting means 221, an input signal fromlevel inverting means 222 and pulse 229. Accordingly, coincidence means223 produces an output signal to reset bistable multivibrators 131, 132and 224 to their respective second output states. Hence, pulse 224 isremoved from an input terminal of coincide'ncemeans 227 and reset relaymeans 228 is deenergized. Consequently, switch means 233 is closed toreset bistable multivibrator 229 to its second output state, and theapparatus'of FIG. 2 is operable to respond to signals subsequentlyapplied thereto.

To summarize the operation of the apparatus schematically represented inFIG. 2, when the pulse I adopts a phase leading relationship withrespect to the pulse II, coincidence means 133 produces pulse 133'having a time duration representative of the phase relationship, andcoincidence means 134 remains in its quiescent state. When, however,pulse I adopts a phase lagging relationship with respect to pulse II,coincidence' means 134 produces pulse 134 having a time durationrepresentative of the phase relationship, and coincidence means 133remains in its quiescent state. The time duration of pulse 133 istransformed to'an analog signal 167' by the first integrating circuitof'integrating means 16, and the time duration ofpulse 134 istransformed to an analog signal 161 by the second integrating circuit ofintegrating means 16, Accordingly-error signals 171' and 172 areselectively storated by grounded capacitance means 171 and-172, re-

. spectively, in accordance with the leading or lagging phaserelationship between pulses I and II. The stored error signal 171 or172' is algebraically combined with a nominal or threshold voltage byamplifier means 181 to produce control signal 181. It is observed thatwhen pulse I is in a phase leading relationship with respect to pulseII,- error signal 171 exhibits a first polarity whereby the controlsignal 181 is effective to produce a retardation in the phase ofpulse 1. However, when pulse I is in a phase lagging relationship withrespect to pulse II, error signal 172 exhibits a second polarity wherebythe control signal 181 is effective to produce a progression in thephase of pulse I.

It is to be understood that variations of the exemplary embodimentillustrated in FIG. 2 are within the contemplation of the presentinvention. For example, integrating means 16 may be comprised of asingle integrating circuit such as a differential integrator thatintegrates the difference between the signals produced by coincidencemeans 133 and 134. Or an algebraic subtracting circuit may couple theoutput terminals of coincidence means 133 and 134 to a singleintegrating circuit. It is recognized that a single integrating circuitobviates the necessaity of a plurality of grounded capacitors includedin storage means 17. Further, bistable multivibrators 131, 132, 229 and230 may be replaced by monostable multivibrators exhibiting satisfacotryduty cycle characteristics. If desired, the nominal or theshold voltagesupplied to amplifier meansv 181 may be derived from a transducercoupled to the second moveable member whereby said transducer produces asignal directly proportional to the velocity of said second moveablemember.

The apparatus of FIG. 2 admits of operating characteristics toaccomodate momentary or intermittent alterations of the relative speedof moveable devices. Prolonged alterations of speed may be nullified byselectively' positioning the adjustable contact 187 of adjustableresistance means 186. The selective positioning of adjustable contact187 is facilitated by the monitoring circuit comprised of amplifiermeans 191), resistance means 191-195 and metering means 198. Ampli fiermeans 190 is similar to aforedescribed amplifier means 181 and maycomprise an operational amplifier. Resistance means 191 couples groundedcapacitance means 172 to amplifier means 190, resistance means 192couples grounded capacitance means 171 to amplifier means 190 andresistance means 193 couples adjustable resistance means to amplifiermeans 190. In addition, resistance means 194 is a feedback resistorinterconnecting the output of amplifier means 190 to the input thereof.Adjustable resistance mean 195 is adapted to be provided with a constantsupply voltage V and may comprise a potentiometer having an adjustablecontact 196. The output of amplifier means 190 is coupled to meteringmeans 198 by current limiting resistance means 197. The metering means198 may comprise a conventional ammeter. It is recognized that theforegoing monitoring circuit is arranged in a configuration similar tothat of control voltage generator 18 and, accordingly, a detailedexplanation of the operation of the monitoring circuit is not deemednecessary.

The purpose of the monitoring circuit is to provide a visual indicationof the operation of the synchronizing apparatus of the presentinvention. If metering means 198 is of the moving coil type, adjustablecontact 196 i is disposed such that the voltage supplied thereby toresistance means 193 is adequate to position the moving coil at apredetermined location on the scale of the metering means 198.

It is expected that, during the normal operation of the apparatus of thepresent invention, the control signal 181' applied to variable frequencygenerating means 19 will admit of the nominal or threshold level, andthe frequency of the periodic signal generated by variable frequencygenerating means 19 will be sufficient to maintain synchronism betweenfirst and second moveable member's. Accordingly, the moving coil ofmetering means 198 will remain at said predetermined location. If, nowthe synchronous relationship between the first and second moveablemembers is disturbed, the error signal 171' applied to resistance means192 by grounded capacitance means 171 will displace the moving coil in afirst direction. However, the control signal 181' will be sufficient toadjust the first moveable member in a manner whereby synchronism isrestored, and the moving coil of metering means 198 will again bepositioned at the predetermined location. Similarly, if an errorsignal172' is applied to resistance means 191, by grounded capacitancemeans 172, the moving coil of metering means 198 will be displaced in asecond direction. Consequently, it is anticipated that the moving coilwill be subjected to occasional displacemerits during the operation ofthe apparatus of the present invention. If, however, the alignment ofthe first moveable member remains out of synchronism with respect to thealignmentof the second moveable member for a prolonged period of time,the moving coil ofmetering means 198 will besubjected to prolonged orfrequent displacements. This indicates that the frequency of theperiodic signal generated by variable frequency generating means 19 isnot sufficient to maintain the desired synchronism between the first andsecond moveable members. Accordingly, adjustable contact 187 must bepositioned in a manner to correspondingly alter the nominal or thresholdvoltage applied thereby .to resistance means 184, whereby the frequencyof the periodic signal produced by variable frequency generating means19 in response to control signal 181" is again sufficient to maintainsynchronism.

FIG. 4 illustrates a system for reproducing information wherein theapparatus of the present invention may be employed, and comprisessynchronizing apparatus 400, as was described in detail in conjunctionwith FIG. 1, a filmstrip 411, optical projecting means 404,photoreceptor means 405, developing means 406, and web 421. Thefilmstrip 411 may comprise a web of microfilm bearing images ofinformation prerecorded thereon, and uniformly spaced sense markingsdistributed along the length thereof. Filmstrip 411 is adapted to betransported from supply spool 412, over guide rolls 413 and 414, normalto slit 403, over capstan 415, guide roll 416, and on to take-up spool417. The capstan 415 is mechanically coupled to electric motor 418,

the latter being coupled to synchronizing apparatus 400. Capstan 415 isadapted to drive take-up spool 417 via spring loaded-belt 418'. Lampmeans 419 is fixedly disposed relative to the filmstrip 411 and is inoptical communication with photocell means 420. Photocell means 420 iselectrically coupled to synchronizing apparatus 400 and is adapted toprovide signals in response to modulations of the radiant energytransmitted by lamp means 419.

Optical projecting means 404 comprises at least one magnifying lensadapted to project images at a predetermined magnification ratio. Theimages projected by optical projecting means 404 may be provided byilluminating the filmstrip 411 that is normal to slit 403. Accordingly,lamp 401 is capable of emitting light of the desired intensity andcondenser lens 402 serves to conduct the light to an area ofconcentration disposed in the vicinity of slit 403.

Photoreceptor means 405 may take the form of an electrophotographicplate comprised of a photoconductive insulating body overlying aconductive backing. The photoconductive insulating body is adapted, inthe well known manner, to have an electrostatic charge applied to itssurface and to selectively dissipate such electrostatic charge upon theexposure thereof to illumination corresponding to a light and darkpattern, such as an information pattern, whereupon a latent image ofsuch pattern is formed. The electrophotographic plate may comprise, forexample, a layer of selenium in the configuration of a drum, asillustrated in FIG. 4. However, as will be apparent to those of ordinaryskill inthe art, the electrophotographic plate may take any convenientform such as an'endless belt. The photoreceptor means 405 is adaptedtobe translated to -a cleaning station 432, for a purpose subseqentlydescribed, and to charging unit 433. Cleaning station 432 may be of thetype described in U.S. Pat. No. 2,751,616 issued to M.I. Turner, Jr., etal. The electrostatic charge applied to the surface of photoreceptormeans 405 may be deposited thereon by charging unit 433 which maycomprise a corona discharge device of the type described in U.S. Pat.No. 2,777,957 issued to L.E. Walkup.

Developing means 406 may comprise any well known form ofelectrophotographic developing apparatus which acts to develop anelectrostatic latent image by the application of electroscopic material407 capable of adhering to the electrostatic charge pattern on the.photoreceptor means 405. The electroscopic material 407 may be appliedto slide 409 from a dispenser 408, whereupon the electroscopic material407 cascades down and over the electrostatic latent image on the surfaceof photoreceptor means 405.

'Web 421 acts as a support surface to receive the developed image fromphotoreceptor means 405 at transfer station 410. Accordingly, the web421 may be of any convenient type, such as paper, and is adapted to betransported from supply spool 422, over guide roll 423, through transferstation 410, over guide roll 424, through heat fusing means 431, guideroll 425 and on to take-up spool 426. The take-up spool 426 is mechamically coupled to electric motor 427. Guide rolls 423 and 424 serve todirect the web 421 into surface contact with photoreceptor means 405 inthe vicinity of charging unit 430 at transfer station 410. Charging unit430 may be similar to aforedescribed charging unit 433. In addition, thefrictional forces between web 421 and photoreceptor means 405 may besuch as to impart a rotational velocity to photoreceptor means 405. Altematively, photoreceptor means 405 may be directly driven by a motormeans, such as electric motor 427, mechanically coupled thereto. Theheat fusing means 431 may be of a type disclosed in U.S. Pat. No.

2,852,651 which issued to Crumrine et al. The web 421 In the operationof the printing apparatus illustrated in FIG; 4, electric motor 418drives capstan 415 at a speed determined by the synchronizing apparatus400 in the now understood manner. It is recognized that, if desired,electric motor 418 may drive take-up spool 417. At the same time,electric motor 427' drives takeup spool 426 at a speed determined bytheoperating characteristics of the electric motor 427. The ratiobetween the speed of take-up spool 426 and the speed of capstan 415should be equal to the magnification ratio of optical projecting means404. As filmstrip 411 is transported, the radiant energy transmitted bylamp 419 is modulated by the sense markings distributed along the lengthof filmstrip 411. Photocell means 420 responds to the modulated radiantenergy to apply signals to synchronizing apparatus 400. Hence, photocellmeans 420 may correspond to first signal producing means 11 of FIG. 1.It should be understood that the radiant energy transmitted by lampmeans 419 may be transmitted directly to photocell means 420, asillustrated in FIG. 4, or may be reflected 411 to photocell means 420.

In a similar manner, as web 421 is transported, the radiant energytransmitted by lamp 428 is modulated by the sense markings distributedalong thelength of web 421. Photocell means 429 responds to themodulated radiant energy to apply signals to synchronizing apparatus400. Hence, photocell means 429 may correspond to second signalproducing means 12 of FIG. 1. The radiant energy transmitted by lampmeans 428 may be reflected from web 421 to photocell means 429, asillustrated in FIG. 4, or may be transmitted directly from lamp means428 to photocell means 429.

from the filmstrip Hence, the signals applied to synchronizing apparatus400 by photocell means 420 and 429 represent the alignments of filmstrip411 and web 421, respectively, from which the respective transportspeeds may be established. The synchronizing apparatus 400 operates inthe manner previously described to synchronize the speed of filmstrip411 with the speed of web 421 by varying the operating speed of electricmotor 418. If

desired, the speed of filmstrip 411 may be synchronized with therotational velocity of photoreceptor means 405. It is, of course,understood that position detecting means other than the aforedescribeddetecting means may be utilized to apply signals to synchronizingapparatus 400.

As photoreceptor means 405 rotates beneath charging unit 433, a uniformelectrostatic charge is'deposited on the surface thereof. The chargedphotoreceptor means 405 is rotated to a location subtending the outputof optical projecting means404. At this location, photoreceptor means405 is exposed to a magnified image of the information recorded onfilmstrip 411. Exposure of the photoreceptor means 405 selectivelydissipates the charge thereon in accordance with the light and darkportions of the character pattern prerecorded on filmstrip 411 andtransmitted by optical projecting means 404, resulting in anelectrostatic latent image of a magnified character pattern.

When photoreceptor means 405 is rotated to the developing means 406, theelectrostatic latent images are developed to form visible images by wellknown treatment with electroscopic material 407. The developed image istransferred to web 421 when photoreceptor means 405 is rotated to thetransfer station 410. The electroscopic material may be transferred toweb 421 by electrostatic transfer, adhesive transfer, or otherconventional electrophotographic transfer techniques. After transfer ofthe image from photoreceptor means 405 to web 421, the photoreceptormeans 405 is rotated to cleaning station 432, where any electroscopicmaterial adhering to photoreceptor means 405 is removed andphotoreceptor means 405 is prepared for re-use in a well known andconventional manner as described in.U.S. Pat. No, 2,751,616.

It should be noted that a plurality of optical projecting means may beselectively provided with varying magnification ratios. If this isdesired, means must be provided to selectively vary the ratio of thespeed of web 421 to the speed of filmstrip 411 in a correspondingmanner. This may be accomplished by the proper positioning of theadjustable contact 187 of control voltage generator 18. In addition,exposure control means including shutter control apparatus may bedisposed in the optical path between optical projecting means 404 andthe photoreceptor means 405.

It should be clear from the foregoing description that the presentinvention is effective to maintain a predetermined alignment betweenfirst and second moveable members to thereby synchronize the velocity ofthe first moveable member with the velocity of the second moveablemember.

While the invention has been particularly shown and described withreference to a plurality of embodiments thereof, it will be obvious tothose skilled in the art that the foregoing and various other changesand modifications in form and details may be made without departing fromthe spirit and scope of the invention. It is, therefore, intended thatthe appended claims be interpreted as including all such changes andmodifications.

What is claimed is: a

1. Apparatus for printing prerecorded information comprising:

a filmstrip bearing said prerecorded information and first uniformlyspaced sense markings distributed along the length thereof;

a web bearing second uniformly spaced sense markings distributed alongthelength thereof;

filmstrip driving means mechanically coupled to said filmstrip fordriving said filmstrip at a controllable velocity;

web driving means mechanically coupled to said web for driving said webat a constant velocity;

first detecting means fixedly disposed relative to said filmstrip fordetecting the passage of each of said first uniformly spaced sensemarkings through a first predetermined position and for generating afirst signal in response to each detected sense marking whereby thefrequency of said generated signals is representative of the velocity ofsaid filmstrip;

second detecting means fixedly disposed relative to said web fordetecting the passage of each of said second uniformly spaced sensemarkings through a second predetermined position and for generating asecond signal in response to each detected sense marking whereby thefrequency of said generated signals is representative of the velocity ofsaid web;

strip driving means in accordance with the amplitude of said controlsignal whereby the velocity of said filmstrip is altered to obtain adesired value; optical means for projecting images of said informationprerecorded on said filmstrip onto photoreceptor means, said opticalmeans comprising magnifying means for projecting an image of saidinformation prerecorded on said filmstrip at a predeterminedmagnification ratio onto said phototreceptor means, said web andfilmstrip being driven at velocities such that the ratio therebetween issubstantially equal to said magnification ratio, and means for printingimages on said web in response to the images projected onto saidphotoreceptor means. 2. The apparatus of claim 1 wherein said controlsignal generating means includes means for selectively varying the ratiobetween the velocity of said filmstrip and the velocity of said web inaccordance with a variation of the ratio of magnification of saidprojected image.

1. Apparatus for printing prerecorded information comprising: afilmstrip bearing said prerecorded information and first uniformlyspaced sense markings distributed along the length thereof; a webbearing second uniformly spaced sense markings distributed along thelength thereof; filmstrip driving means mechanically coupled to saidfilmstrip for driving said filmstrip at a controllable velocity; webdriving means mechanically coupled to said web for driving said web at aconstant velocity; first detecting means fixedly disposed relative tosaid filmstrip for detecting the passage of each of said first uniformlyspaced sense markings through a first predetermined position and forgenerating a first signal in response to each detected sense markingwhereby the frequency of said generated signals is representative of thevelocity of said filmstrip; second detecting means fixedly disposedrelative to said web for detecting the passage of each of said seconduniformly spaced sense markings through a second predetermined positionand for generating a second signal in response to each detected sensemarking whereby the frequency of said generated signals isrepresentative of the velocity of said web; comparison means coupled tosaid first and second detecting means for generating signals indicativeof the phase relationship between said first and second signals; controlsignal generating means coupled to said comparison means for generatinga control signal having an amplitude determined by the signals generatedby said comparison means; feedback meanS coupled to said filmstripdriving means and responsive to said control signal for adjusting theoperating characteristics of said filmstrip driving means in accordancewith the amplitude of said control signal whereby the velocity of saidfilmstrip is altered to obtain a desired value; optical means forprojecting images of said information prerecorded on said filmstrip ontophotoreceptor means, said optical means comprising magnifying means forprojecting an image of said information prerecorded on said filmstrip ata predetermined magnification ratio onto said phototreceptor means, saidweb and filmstrip being driven at velocities such that the ratiotherebetween is substantially equal to said magnification ratio, andmeans for printing images on said web in response to the imagesprojected onto said photoreceptor means.
 2. The apparatus of claim 1wherein said control signal generating means includes means forselectively varying the ratio between the velocity of said filmstrip andthe velocity of said web in accordance with a variation of the ratio ofmagnification of said projected image.